THIS ITEM IS A SET OF TWO GTD THREAD GO/NO GO GAUGES, UTILIZED FOR ACCURATE THREAD VERIFICATION AS A TOOLING AND ACCESSORIES COMPONENT. THE SET INCLUDES TWO DISTINCT MODELS: THE GTD B-87370 AND THE GTD B-87366. THE B-87370 MODEL FEATURES A LO – PD OF 2.9552 AND IS SPECIFIED FOR 3-16, UN-3A THREADS. THE B-87366 MODEL FEATURES A LO – PD OF 2.9124 AND IS SPECIFIED FOR 3-8, UN-3A THREADS.